Note 6 — Chapter I

There is little difference between the action of an oar in sculling and that of the modern screw-propeller, which is fast superseding the paddle-wheel in all ocean-going steamers: the one has an alternate lateral motion, like the tail of a fish; the other is rotatory, but with the same effect. It may be added that fishes often have the power of “feathering” their tails, by puckering their lobes in their forward motion, and expanding them on their return, so as to displace as little water as possible, while they, at the same time, rely for their advancement on the reaction of the water in the direction of their body. These points have been carefully considered in the construction and arrangement of the blades of the screw, as well as the important fact that the tail of the fish or the sweep of an oar in their motions displace a quantity of water, great in proportion to the length of the instruments employed; and further, that it is by the resistance the water makes to this displacement by the oar or tail, in their continued oscillation, coming as these do from their extreme sweep to the axis of the boat or fish, that either is urged forward.